Set in a modern day survival-horror universe, the co-operative gameplay of L4D casts four Survivors in an epic struggle against hordes of swarming zombies and terrifying Boss Infected mutants. Valve’s next generation AI technology, allows for games of 1 to 8 players. Players can play as a Survivor or as one of four types of “Boss Infected,” each of whom possess a unique mutant ability such as a 50-foot tongue lasso or a giant belly full of explosive methane gas.